Governments worldwide adopt e-government model and use ICT and particularly the Web as a key vehicle. This means the full integration of new technologies for transforming the public administrations and facilitating drastically the information flow among different governmental agencies, citizens and businesses. Interoperability appears as the mean for accomplishing the inter-linking of information, systems, applications and ways of working not only within governments but also in their interaction with the administration, enterprises and public sector. The paper highlights the critical role of interoperability and investigates the way it can be incorporated into e-government domain in order to provide efficient and effective e-services. It also describes issues-steps associated to interoperability, depicts the arisen technical dimensions, proposes solutions when possible, and discusses its effectiveness. Finally, it illustrates the future trends in the field and suggests directions that may produce new scientific results.